In many clutch applications, it is necessary or desirable to provide clutch overload protection for the equipment being driven by the clutch in order to protect such equipment and/or to insure safe operation of the equipment. Such torque overload protection can provided in a number of differing ways. A clutch designed to slip at a predetermined torque level may provide the necessary protection, but it suffers from the disadvantage that it is relatively difficult to precisely control the torque level at which it slips, and in addition, slip produces excessive wear of the clutch engagement surfaces. Also, these clutches do not disengage cleanly; that is, a certain level of torque will continue to be transmitted by the slipping surfaces.
A torque overload shear pin arrangement, in which the driving members are rendered incapable of transmitting drive by the shear failure of the pin or other element, has the disadvantage that the equipment cannot be reengaged without shut down and replacement of the sheared element.
Other arrangements have included clutches which are caused to disengage by various camming arrangements upon achievement of a predetermined torque level of transmission through the unit. An example of this method is disclosed in U.S. Pat. No. 3,584,715. The disadvantage of this approach is that often the camming arrangement involves the engagement of the camming surfaces of a configuration such as to preclude the reengagement of the clutch at relatively high speeds, due to possible damage to the camming surfaces. This comment applies equally well to applications which utilize tooth type clutches.
A second torque overload feature disclosed in the forementioned U.S. Pat. No. 3,584,715, issued to the present inventor, includes a provision for a torque sensing ring which is caused to be rotated relative to a second ring member against the force of a bias spring. The resultant relative rotation produces an axial movement of the first ring by a sliding movement on a spline member against the bias of a restraining spring. The axial movement, upon continuing for a predetermined extent, triggers a switching arrangement which deenergizes the clutch. While offering many advantages, this particular installation requires a relatively costly torque sensing arrangement, which, in addition to the existing components of the clutch, increases the expenses of manufacture. Furthermore, the axial movement is not entirely friction free and affects the accuracy of maintaining the torque at which the clutch will be deenergized.
Accordingly, it is the object of the present invention to provide a clutch incorporating a torque overload arrangement in which the torque level at which the clutch is released may be precisely controlled.
It is yet another object of the present invention to provide such a clutch in which the clutch may be reengaged at relatively high speeds without damage to the clutch.
It is a still further object of the present invention to provide such a torque overload arrangement which does not necessitate expensive additional components to the basic design of the clutch such as to enable the clutch unit to be manufactured at relatively low cost.